A revisited method for Mg purification and isotope analysis using cool-plasma MC-ICP-MS

Abstract

Magnesium is an important element in both the lithosphere and biosphere. Many previous studies have focused on directly tracing Mg cycles using Mg isotopes, and various methods for Mg purification and isotopic measurement have been previously elucidated. Here, we present a newly developed Mg separation method, along with a verification of the method by measuring the Mg isotope composition (expressed as δ²⁶Mg relative to DSM-3) of various standard materials. All matrix cations causing significant mass bias were effectively removed through this Mg purification methodology, resulting in an Mg yield of ∼100% when the matrix concentration did not exceed 5% of the Mg concentration. Following this, Mg isotope ratios were measured using a Neptune MC-ICP-MS equipped with an X-cone under cool plasma conditions, reducing interferences while optimizing instrumental sensitivity. The long-term reproducibilities of the δ²⁶Mg_DSM-3 values of CAM-1 and SRM980 were −2.65 ± 0.08 (2σ, n = 14) and −4.34 ± 0.08‰ (2σ, n = 10), respectively. The Mg isotopic compositions in a variety of international rock and seawater standards were between −0.17 and −0.86‰, in good agreement with the reported values. These results indicate that the Mg purification method presented here, followed by isotope analysis using cool plasma, is an efficient high-precision method for determining Mg isotope compositions.